Digital systems and methods for high precision control in nuclear reactors

ABSTRACT

Control rod drives include all-digital monitoring, powering, and controlling systems for operating the drives. Each controlling system includes distinct microprocessor-driven channels that independently monitor and handle control rod drive position information reported from multiple position sensors per drive. Controlling systems function as rod control and information systems with top-level hardware interfaced with nuclear plant operators other plant systems. The top-level hardware can receive operator instructions and report control rod position, as well as report errors detected using redundant data from the multiple sensors. Positional data received from each drive is multiplexed across plural, redundant channels to allow verification of the system using independent position data as well as operation of the system should a single channel or detector fail. Control rod drives are capable of positioning and detecting position of control elements in fine increments, such as 3-millimeter increments, with plural position sensors that digitally report drive status and position.

BACKGROUND

FIG. 1 is a cross-sectional illustration of a related art control roddrive 10 useable in a nuclear reactor. For example, related art controlrod drive 10 may be a Fine Motion Control Rod Drive (FMCRD) as used innext generation BWRs like ESBWRs. As shown in FIG. 1, control rod driveis housed outside, such as below, reactor pressure vessel 1, where drive10 inserts or withdraws a control element, such as a control blade (notshown), attached thereto via bayonet coupling 15. Hollow piston 16connects to bayonet coupling 15 and is vertically moveable inside of anouter tube in drive 10. Drive 10 includes ball screw 11 coupled withball nut 12 that drives screw 11 vertically when rotated, such thathollow piston 16, bayonet coupling 15, and the control element attachedthereto may be positioned with precision at desired positions in anuclear reactor core. During scram, hollow piston 16 may be lifted offball nut 12 by hydraulic pressure in the outer tube, permitting rapidmovement and insertion of the control element. A magnetic coupling 17pairs internal and external magnets to rotate ball screw 11 across apressure barrier, and a motor and brake 19 mounted below drive and stopmagnetic coupling 17 to desired positioning.

Power and control is provided to control rod drive by a Rod Control &Information System (RC&IS) that in varying conventional designs uses amix of analog systems and digital transducers, including resolvers andsynchros and encoders, and any required analogue-to-digital converters,coupled to motor and brake 19 to provide position detection, control,and power to the same. Several existing mixed analog and digital systemsare able to detect and resolve position of associated control elementsto several centimeters, with coarser position control. Relateddescriptions of drive 10 and FMCRD technology are found in GE-HitachiNuclear Energy, “The ESBWR Plant General Description,” Chapter 3—NuclearSteam Supply Systems, Control Rod Drive System, Jun. 1, 2011,incorporated herein by reference in its entirety.

SUMMARY

Example embodiments include all-digital control rod drives andassociated systems for monitoring, powering, and controlling the drives.Control and information systems may be divided into distinct channelswith switches and controls of each channel performing independent andredundant control rod drive monitoring and controlling. Control andinformation systems may separately be divided among main control logicassociated with plant operators and top-level input from other plantsystems, remote cabinet equipment including multiplexed data handlingfor transmission to the main control logic, fine motion controllersassociated with each control rod drive, and the control rod drivethemselves. Each of these subsystems may pass control rod drive positioninformation from multiple position sensors to the plant operators andother plant systems. Each piece of position information from anindividual sensor, such as a digital position transducer, may be handledby one of the distinct channels of the control and information systems.Because the entire system, including control rod drives and control andinformation systems, may work with digital information on computerhardware processors and associated memories and busses, nodigital-to-analog converter is necessary. By connecting and multiplexingeach channel throughout the system, controllers associated with eachchannel may verify accuracy of position information with controllers ofother channels, and redundant commands and data may be transmitted andreceived even if one channel or sensor fails.

Control rod drives useable in example embodiments include fine motioncontrol rod drives capable of positioning and detecting position ofcontrol elements in very fine increments, such as 3-millimeterincrements, such as with rotating servo motors. Example control roddrives may further include several position sensors that digitallyreport control rod drive status and insertion position in these fineincrements. A single control and information system may receive themultiple position sensor readings from multiple control drive systemsand control the same using appropriate powering and control signals toachieve desired control rod positioning.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Example embodiments will become more apparent by describing, in detail,the attached drawings, wherein like elements are represented by likereference numerals, which are given by way of illustration only and thusdo not limit the terms which they depict.

FIG. 1 is an illustration of a related art nuclear control rod drive.

FIG. 2 is a schematic of a fine motion control rod drive motor and itsmotor control cabinet.

FIG. 3 is a schematic of an example embodiment digital rod control andinformation system.

DETAILED DESCRIPTION

Because this is a patent document, general broad rules of constructionshould be applied when reading it. Everything described and shown inthis document is an example of subject matter falling within the scopeof the claims, appended below. Any specific structural and functionaldetails disclosed herein are merely for purposes of describing how tomake and use examples. Several different embodiments and methods notspecifically disclosed herein may fall within the claim scope; as such,the claims may be embodied in many alternate forms and should not beconstrued as limited to only examples set forth herein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited to any order by these terms. These terms are used only todistinguish one element from another; where there are “second” or higherordinals, there merely must be that many number of elements, withoutnecessarily any difference or other relationship. For example, a firstelement could be termed a second element, and, similarly, a secondelement could be termed a first element, without departing from thescope of example embodiments or methods. As used herein, the term“and/or” includes all combinations of one or more of the associatedlisted items. The use of “etc.” is defined as “et cetera” and indicatesthe inclusion of all other elements belonging to the same group of thepreceding items, in any “and/or” combination(s).

It will be understood that when an element is referred to as being“connected,” “coupled,” “mated,” “attached,” “fixed,” etc. to anotherelement, it can be directly connected to the other element, orintervening elements may be present. In contrast, when an element isreferred to as being “directly connected,” “directly coupled,” etc. toanother element, there are no intervening elements present. Other wordsused to describe the relationship between elements should be interpretedin a like fashion (e.g., “between” versus “directly between,” “adjacent”versus “directly adjacent,” etc.). Similarly, a term such as“communicatively connected” includes all variations of informationexchange and routing between two electronic devices, includingintermediary devices, networks, etc., connected wirelessly or not.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude both the singular and plural forms, unless the languageexplicitly indicates otherwise. It will be further understood that theterms “comprises,” “comprising,” “includes,” and/or “including,” whenused herein, specify the presence of stated features, characteristics,steps, operations, elements, and/or components, but do not themselvespreclude the presence or addition of one or more other features,characteristics, steps, operations, elements, components, and/or groupsthereof.

The structures and operations discussed below may occur out of the orderdescribed and/or noted in the figures. For example, two operationsand/or figures shown in succession may in fact be executed concurrentlyor may sometimes be executed in the reverse order, depending upon thefunctionality/acts involved. Similarly, individual operations withinexample methods described below may be executed repetitively,individually or sequentially, so as to provide looping or other seriesof operations aside from single operations described below. It should bepresumed that any embodiment or method having features and functionalitydescribed below, in any workable combination, falls within the scope ofexample embodiments.

The inventors have recognized that existing locking collet piston andmagnetic jack type control rod drives lack precision, being able to movein increments of 6 inches or more. Typical ESBWRs and other large,natural-circulation-dependent reactors require greater precision forreactivity control. Related FMCRD, such as in the ABWR, while havinggreater precision, are operated using analog sensors such as synchrosand servos, which require an analog-to-digital converter for control.The use of analog sensors results in decrease of precision accuracy.Moreover, controls for FMCRD need to have very high reliability innuclear applications, and single-channel analog controls represent animpermissible failure risk for lack of redundancy. Example embodimentsdescribed below address these and other problems recognized by theInventors with unique solutions enabled by example embodiments.

The present invention is a control rod drive control and informationsystem. In contrast to the present invention, the small number ofexample embodiments and example methods discussed below illustrate justa subset of the variety of different configurations that can be used asand/or in connection with the present invention.

Example embodiment control rod drive (CRD) control and informationsystems are useable with several different types of CRDs. Exampleembodiments are further useable with high-precision CRDs, includingFMCRDs. Further, co-owned applications 62/361,628, filed Jul. 28, 2016by Morgan et al., 62/361,625, filed Jul. 13, 2016 by Morgan et al., and62/361,604, filed Jul. 13, 2016 by Morgan et al. are incorporated hereinby reference in their entireties. These incorporated applicationsdescribe high-precision CRDs that are useable with example embodiments;for example, example embodiment control systems may be interfaced with,and control, the control rod drives disclosed in the incorporatedapplications.

FIG. 2 is a schematic of FMCRD 10 where motor 19 and output of the FMCRDinterface with an example embodiment system 100. As shown in FIG. 2,motor 19 may receive power and operative signals from a motor controlcabinet 21 over motor interface 26. For example, motor interface 26 maybe radiation-hardened power cables that deliver electrical power, suchas three-phase pulse-width modulated electrical signals, and/orinformation like speed controls to motor 19 in challenging environmentssuch as operating nuclear reactor environments. Fine motion motorcontroller 20 may receive such power from a plant power source 25,including main plant electrical bus, local battery, emergencygenerators, or any other source of power.

Motor controller 20 is configured to power motor interface 26 for bothvery fine intervals and very large power jumps. In this way, motor 19may be powered to move a control blade attached to FMCRD 10 at veryprecise intervals, such as 3 millimeter vertical insertions orwithdrawals, as well as rapid, large insertion strokes for shutdown. Forexample, motor 19 may be a servo motor that is controllable up to ¼^(th)of one revolution of a ball screw in FMCRD 10 that can self-brake andprovide long-term static torque. A full revolution may equate to 12millimeters of vertical control element movement, so positioning on anorder of a few millimeters is possible. Delivery of a precise amount ofpower through motor interface 26 may thus achieve desired precise motoractuation and control element positioning.

FMCRD 10 may include multiple position detectors 18 a and 18 b, such asprecise digital transducers that can determine an exact verticalposition of ball nut 12 and/or other connective structures to report anaccurate position of a control element within one-thirty-sixth of amillimeter. Position detectors 18 a and 18 b may be redundant or measureposition of related structures as a verification of control elementpositioning. For example, two digital transducers as position detectors18 a and 18 b may be coupled directly to a power output or shaft ofmotor 19 that encode rotations of the same to digitally represent motor19 position and thus control element position. Because positiondetectors 18 a and 18 b may give digital output, informationalpositional signal interfaces 27 a and 27 b may be any connection capableof carrying digital signals, including fiber optic cable, coaxialcables, wireless signals, etc., separate or combined with motorinterface 26.

Fine motion motor controller 20 includes two channel interfaces 28 a and28 b each configured to receive digital position information from anassociated one of detectors 18 a and 18 b via positional signalinterfaces 27 a and 27 b. Channel interfaces 28 a and 28 b mayseparately handle individual positional signals and control inputs so asto preserve integrity of a redundant system and allow different signalsto be verified against one another without intermixing or single failureaffecting both signals. Fine motion motor control cabinet 21 housingmotor controller 20 and various interfaces and communicative connectionsmay be local or remote from FMCRD 10. Because all components of cabinet20 may be digital with no analog-to-digital converter, cabinet 20 may berelatively small and better hardened against an operating nuclearreactor environment.

FIG. 3 is a schematic diagram of an example embodiment digital rodcontrol and information system (RC&IS) 100. As shown in FIG. 3, exampleembodiment RC&IS 100 interfaces with a FMCRD 10 and fine motion motorcontroller 20 (FIG. 2) through remote links 37 a and 37 b. RC&IS 100 maybe located closer to an operator or control room, outside of containmentand remote from FMCRD 10 and its motor control cabinet 21 (FIG. 2), inwhich case remote links 37 a and 37 b may be any kind of digital dataconnection, including higher-reliability fiber optic cables or wirelessconnections. Remote links 37 a and 37 b together communicatedual-channel positional data from an FMCRD, such as digital positionaldata generated by position detectors 18 a and 18 b for redundantposition determination of individual control elements.

RC&IS 100 includes remote communication cabinet equipment 110 networkedwith an RC&IS main control logic 111 that is configured to receive input200 from operators and other plant systems for control element operationand positioning. RC&IS 100 is completely digital, using microprocessors,field-programmable gate arrays, and digital communications for higherreliability and less space requirement. Cabinet equipment 110 may be allstored in a discreet and smaller cabinet remote or local to a controlrod drive. For example, cabinet equipment 110, lacking anyanalog-to-digital converter, may fit in a relatively small space andhandle control element operations for a quarter of a nuclear core.Moreover, all-digital RC&IS 100 is less susceptible to noise andvibration found in an operating nuclear operating environment and thuscan be located anywhere in a nuclear plant and can perform self-testingand alerting functions to maintain desired operations with lower failurerates than analog equipment.

Example embodiment RC&IS 100 is configured to handle and control anFMCRD with dual, redundant inputs to maintain operations in the case ofsingle-channel failure, such as if a single position detector becomesunusable or signals are lost from one channel in example embodiments. Asshown in FIG. 3, RC&IS 100 includes two independent channels 120 and 130in its cabinet equipment 110, each in communication with an individualposition data source such as remote links 37 a and 37 b. Although shownin communication with a single set of remote links 37 a and 37 b, it isunderstood that multiple FMCRDs and related motor controls may be inputinto and controlled by cabinet equipment 110, including an entire corequadrant's worth of control drives.

Each channel 120 and 130 independently handles distinct digital positionand operation signals; however, channels 120 and 130 are also connectedin order to verify and potentially replace one another. Buscommunications 115 between all elements of channels 120 and 130 may betypical digital communications lines, including internal computer buses,motherboard connections, wired connections, or wireless connections.Each channel 120 and 130 includes multiplexed and redundant switches121, 122, 124, 131, 132, and 134. Switches 122, 124, 132, and 134 mayreceive positional data and issue motor command signals, as well asother data, for each control rod drive associated with RC&IS 100. Asshown by bus communications 115, switches 121 and 122 associated withchannel 120 may include connection to switches 131 and 132 of the otherchannel 130. Thus, if a switch fails in either channel, or if otherchannel components become inoperative, the operative channel andswitches therein may still receive, transmit, and otherwise handle allcontrol information.

Each channel 120 and 130 includes a controller 123 and controller 133,respectively. The controllers 123 and 133 may receive, buffer, issue,and interpret control rod drive operational data. For example,controllers 123 and 133 may receive rod movement commands from RC&IScontrol channel controllers 165 and 155, and such commands may beinterpreted and sent to one or more motor controllers 20 (FIG. 2)through remote links 37 a and 37 b. Motor controller 20 (FIG. 2) maythen provide power transmission to a motor 19 through motor interface 21(FIG. 2) to achieve desired driving, braking, and position fromdetectors 18 a and 18 b (FIG. 2), interpreted for operator readout.

As shown in FIG. 3, controllers 123 and 133 may also perform comparisonof rod movement commands from the RC&IS control logic controllers 155and 165 to ensure that inconsistent rod movement commands do not resultin rod movement. Switches 124 and 134 may provide redundant data linksbetween each RC&IS logic channel controller 165 and 155, and each remotecabinet controller 123 and 133. Switches 122, 132, 121, and 131 mayprovide redundant data links between each controller 123 and 133 andmultiple motor controllers 20 (FIG. 2).

As shown in FIG. 3, each controller 123 and 133 in channel 120 and 130interfaces with an input/output switch 124 and 134 for sending andreceiving operational data to operator controllers in RC&IS main controllogic 111. Because main control logic 111 interfaces with several otherplant safety systems and operator controls, control logic 111 istypically located in or near a control room or other plant operatorstation. Input/output switches 124 and 134 multiplex control commandsand information from both channels over main logic interfaces 140 tomain control logic 111. For example, main control logic may include twoor more main RC&IS channel controllers 165 and 155, each with twoswitches 161, 162, 151, and 152. Main logic interfaces 140 may bemultiplexed to provide digital information and control data from bothchannels 120 and 130 to each switch 151, 152, 161, and 162. In this way,main RC&IS channel controllers 155 and 165 may have redundant switchesthat each have access to both channels associated with each control roddrive.

Main RC&IS channel controllers 155 and 165 receive and implementoperator feedback and input, including control element positioningcommands, as well as input 200 from other plant systems, such as plantsteady-state information or trip alerts. Because each main controller155 and 165 receives redundant control and command data, and can issueredundant commands to independent channels 120 and 130, eithercontroller 155 and 165 may be used to report on and operate all aspectsof a control drive, regardless of failure of the other controller and/orof channel equipment or position reporting equipment.

Similarly, because main RC&IS channel controllers 155 and 165 maythemselves be connected and communicate through an internal bus or otherplant communicative connections, controllers 155 and 165 may verifypositional and operational data received as well as operator inputsbetween themselves. Controllers 155 and 165 may be configured to detectdiscrepancies between information received from either channel 120 and130, as well as inputs 200 or operator controls received by them both.Upon detection of a discrepancy, an operator may be notified and/or achannel may be identified as out-of-service. For example, an operator orplant control system may input a very fine control elementrepositioning, such as 3 mm, for a single control blade, and system 100may receive and process the move, resulting in rod movement commands tothe motor controller 20 and appropriate power and signaling transmittedto motor 19 from the motor controller 20 through motor interface 26(FIG. 2). Position detectors 18 a and 18 b (FIG. 2) may then reportdigital, accurate rod repositioning information, which may be processedby the motor controller 20 and transmitted to the remote controllers 123and 133, which may interpret and transmit the rod repositioninginformation to the main controllers 165 and 155. Main controllers 165and 155 may verify this position data from both channels and thusdetectors, and ensure it reflects the input command. Because channelcontrollers 155 and 165 are themselves digital, such analysis andnotification or disregarding of bad channel data may be implemented assimple programming or hardware structuring in microprocessors ofcontrollers 155 and 165. Each channel of RC&IS controller logic, 155 and165, may contain one or more microprocessors, such as three redundantmicroprocessors R, S, and T each performing the same RC&IS logiccomputations independently and asynchronously of each other. Redundantmicroprocessors in each RC&IS control logic channel, 165 and 155 mayensure detectability and continuity of rod control logic functions inthe presence of a single microprocessor failure.

Example embodiment RC&IS 100 is end-to-end digital, handling data andcommands received directly from digital inputs and outputs. Suchdigitization allows for a smaller footprint, faster analysis and action,less susceptibility to noise, vibration, heat, and radiation damage,finer motor control and monitoring, and easier handling ofmultiple-channel data for redundancy and verification in control roddrive operation. Further, connections among various components, such asby internal connections 115 or connections 140 between potentiallyremotely-situated cabinet 110 and main logic 111, may be reliablecommunicative connections between systems, including internal busses onmotherboards, fiber optic cables, etc.

Example embodiments and methods thus being described, it will beappreciated by one skilled in the art that example embodiments may bevaried and substituted through routine experimentation while stillfalling within the scope of the following claims. For example, althoughonly one FMCRD 10 is shown schematically connected to example embodimentsystem 100, use of multiple different FMCRDs, as well as other types ofcontrol rod drives for a variety of different reactor sizes andconfigurations are compatible with example embodiments and methodssimply through proper dimensioning of example embodiments—and fallwithin the scope of the claims. Such variations are not to be regardedas departure from the scope of these claims.

What is claimed is:
 1. A digital system for operating a control roddrive in a nuclear power plant, the digital system comprising: a firstchannel controller configured to receive digital position informationfrom a first control rod drive position sensor in the control rod drive;a second channel controller configured to receive digital positioninformation from a second control rod drive position sensor in thecontrol rod drive, wherein the first channel controller and secondchannel controller are configured to report a position of the controlrod based on the received digital position information from the firstand the second control rod drive position, and wherein the system doesnot include any digital-to-analog converter.
 2. The system of claim 1,wherein the first channel controller includes a first channel and afirst main RC&IS channel controller, and wherein the second channelcontroller includes a second channel and a second main RC&IS channelcontroller.
 3. The system of claim 2, further comprising: a remoteconnection multiplexing the first channel and the second channel intothe first and the second main RC&IS channel controllers such that eachof the first channel and the second channel is digitally connected toall of the first and the second main RC&IS channel controllers.
 4. Thesystem of claim 3, wherein the remote connection is fiber optic cable.5. The system of claim 3, wherein the first and the second main RC&ISchannel controllers each include two switches, and wherein the firstchannel and the second channel each include an import/output switchconnected by the remote connection to all of the two switches of thefirst and the second main RC&IS channel controllers.
 6. The system ofclaim 2, wherein the first and the second channel are in a cabinetremote from the control rod drive and from the first and the second mainRC&IS channel controllers in the nuclear power plant.
 7. The system ofclaim 6, wherein the first and the second main RC&IS channel controllersare operable from a control room of the nuclear power plant and receiveinformation from other systems of the nuclear power plant.
 8. The systemof claim 1, wherein the first channel controller and the second channelcontroller are further configured to transmit operation signals to thecontrol rod drive.
 9. The system of claim 1, further comprising: thecontrol rod drive, wherein the control rod drive is a fine motioncontrol rod drive having a servo motor moving in 3 millimeter verticalincrements.
 10. The system of claim 9, wherein the first control roddrive position sensor and the second control rod drive position sensorare paired with the motor and are digital transducers that measure arotational position of the motor.
 11. The system of claim 9, furthercomprising: a fine motion motor controller interfaced between thecontrol rod drive and the first and the second channel controllers. 12.The system of claim 11, wherein the first channel controller and thesecond channel controller are further configured to transmit operationsignals to the control rod drive, and wherein the fine motion motorcontroller delivers electrical power to the motor based on thetransmitted operation signals.
 13. The system of claim 11, wherein thefirst and the second channel controllers are further configured toreceive digital position information from a plurality of the firstcontrol rod drive position sensors and the second control rod driveposition sensors coupled to a plurality of the control rod drives.
 14. Afully digital control rod drive in a nuclear power plant, the controlrod drive comprising: a servo motor configured to vertically drive acontrol rod by rotating; a first digital position transducer coupled tothe servo motor; and a second digital position transducer coupled to theservo motor, wherein the first and the second digital positiontransducers measure to one-three-hundred-sixtieth of a rotation of theservo motor, which corresponds to approximately one-thirty-sixth of amillimeter of vertical control rod movement, and wherein the first andthe second digital position transducers independently transmit digitalrotation information of the servo motor.
 15. The control rod drive ofclaim 14, further comprising: a RC&IS communicatively connected to thefirst and the second digital position transducers to receive the digitalrotation information, wherein the RC&IS is further configured to reportcontrol rod position and receive plant and operator input.
 16. Thecontrol rod drive of claim 15, further comprising: a fine motion motorcontroller interfaced between the control rod drive and the first andthe second channel controllers, wherein the fine motion motor controllerincludes a power connection to the servo motor.
 17. The control roddrive of claim 15, wherein the RC&IS includes a first channel controllerand a second channel controller,
 18. The control rod drive of claim 15,wherein the first channel controller includes a first channel and afirst main RC&IS channel controller, and wherein the second channelcontroller includes a second channel and a second main RC&IS channelcontroller.
 19. The control rod drive of claim 18, further comprising: aremote connection multiplexing the first channel and the second channelinto the first and the second main RC&IS channel controllers such thateach of the first channel and the second channel is digitally connectedto all of the first and the second main RC&IS channel controllers. 20.The control rod drive of claim 14, wherein the drive is nowherecommunicatively connected to any digital-to-analog converter.